1. Field of the Invention
The present invention relates to a double-wishbone type suspension system for a front wheel of an automobile vehicle.
2. Description of the Related Art
This kind of double-wishbone type suspension system is disclosed, for example, in a Japanese monthly journal "Motor Fan", June, 1987, at page 79, and generally includes a hub carrier for rotatably supporting a front wheel of a vehicle, and upper and lower link devices for connecting upper and lower ends of the hub carrier to a vehicle body, respectively. The lower link device includes a link element which is to be applied with a steering force for causing rotation of the hub carrier and resultant steering of the front wheel. A variety of double-wishbone type suspension systems are known, depending upon the manner for supporting the upper and lower link devices in the fore-and-aft direction of the vehicle body.
However, according to conventional double-wishbone type suspension system, the kingpin axis about which the hub carried and hence the front wheel are rotated is theoretically fixed even during the steering operation, as can be readily appreciated from the publication mentioned above. The camber characteristic of the vehicle during the front wheel steering operation is thus uniquely determined by the caster angle, i.e. an inclination angle of the kingpin axis with reference to the fore-and-aft direction of the vehicle body.
It is well known that the cornering performance of the vehicle during the steering operation of the front wheels is primarily influenced by the cornering power of an outer front wheel which is situated on outer side with reference to the cornering center. Furthermore, the rolling of the vehicle body during the steering operation tends to increase the camber angle of the outer front wheel and hence the tire inclination angle with reference to the ground surface in the positive camber direction, thereby lowering the cornering power of the outer front wheel. In consideration of these factors, it is required for the camber characteristic of the outer front wheel to exhibit a negative camber tendency during the steering operation.
For adapting the known double-wishbone type suspension systems to the above-mentioned requirement, it has been generally considered necessary to increase the kingpin axis inclination angle (i.e. caster angle) with reference to the fore-and-aft direction of the vehicle body. However, the kingpin axis setting for realizing an increased caster angle often results, not only in increased steering force, i.e. the operational force required for steering the front wheels, but also in generation of a force component which tends to lift the front wheels with an apparent relative decrease in the body height of the vehicle body front section, thereby significantly deteriorating a natural steering feel.